An organic photovoltaic device is a photovoltaic device that uses organic materials, such as conductive polymers or small organic molecules, to convert light into an electrical current. Organic photovoltaic devices can be used over a range of wavelengths for converting light into electrical energy. Organic photovoltaics devices have drawn interest for use as a source of renewable energy due to their potential compatibility with high throughput, roll-to-roll fabrication processes as well as low material cost. Conventional organic photovoltaic devices often utilize a planar heterojunction (PHJ) device architecture, in which two organic materials with dissimilar electronic properties are layered together.
FIG. 13 is an example of a planar heterojunction organic photovoltaic cell (OPV) 100. The organic photovoltaic cell 100 includes an anode 102, a cathode 104, a donor organic semiconductor layer 106 and an acceptor organic semiconductor layer 108. In an organic semiconductor, photon absorption can lead to the formation of tightly bound, mobile electron-hole pairs known as excitons. Excitons generated in either the donor or acceptor layers 106, 108 diffuse to an interface 110 between the layers. This interface is known as a donor-acceptor (D-A) heterojunction. Due to differences in electron affinity and ionization energy between the donor layer 106 and acceptor layer 108, an energy level offset exists at the interface. If this offset exceeds the exciton binding energy (i.e., the energy required to bind the electron-hole pair together), the excitons can dissociate. Following dissociation, the electron and hole charge carriers can be collected at their respective electrodes.